In many cases the energy consumption of an electronic device, such as a digital processor circuit, is a critical issue. For example, technologies such as the Internet-of-Things “IoT”, the Industrial Internet “II”, and the Internet-of-Everything “IoE” are on the threshold of a massive breakthrough, and the major drivers behind the breakthrough are ubiquitous wireless processing nodes. However, the energy consumption of transmitting a bit across a given distance does not scale with Moore's law as advantageously as the digital processing within a wireless node. Therefore the energy cost of wireless transmission will proportionally grow when compared to digital processing. Increasing the energy efficiency thus requires increasing the amount of intra-node processing in order to minimize the wireless transmission of data. Therefore, the processor and the digital signal processing “DSP” will become one of the, if not the, most important parts to be optimized. This will be compounded by the increasing functionalities of the wireless node, such as e.g. Machine Learning, Video, etc.
For example, in conventional digital Complementary Metal Oxide Semiconductor “CMOS” designs, the operating voltage i.e. the power supply voltage VDD is typically 1 Volt or greater. The energy consumption indicated by the power consumption is substantially quadratically dependent on the operating voltage VDD, i.e. the power consumption is substantially proportional to VDD2. Therefore, there is a strong motivation to reduce the operating voltage VDD for a wide range of applications from energy-constrained systems, e.g. the Internet-of-Things “IoT”, to thermal-constrained systems, e.g. servers. There is a lower bound on the operating voltage VDD due to: a) functional limitations of the technology such as e.g. the CMOS technology and b) performance limitations such as e.g. limitations on the operating speed. By operating slightly above the lower bound of the operating voltage VDD, or near the threshold voltage, “NTV”, the digital design is robust, has low energy consumption, and has a good performance. Thus, there is an increasingly large amount of researchers and companies building digital NTV designs. In some cases and especially in conjunction with central processing units “CPU”, the operating voltage is often called core voltage.
A potential market of the NTV is in near-future electronics for applications such as the above-mentioned IoT and wireless wellbeing and healthcare. Growth in the healthcare industry is expected to be one of the major drivers and is expected to have a positive impact on embedded system demand. This can be attributed to the substantial number of embedded systems used in medical devices such as blood glucose monitors.
Ideally, an electronic system would be able to scale its operation from the nominal operating voltage down to the NTV. However, reducing the operating voltage below the threshold voltage results in a dramatic loss in performance and in practice may lead to functional failure. Therefore, in order to operate at the NTV, there needs to be a method to identify where the threshold voltage is located. The method is advantageously dynamic since the threshold voltage in for example CMOS devices changes with both local and global variations, e.g. temperature. In addition, a body bias is used in modern CMOS to intentionally move the threshold voltage. In a known technical solution for reducing the energy consumption, the operating voltage VDD is determined with the aid of a look-up table which gives the value of the operating voltage as a function of operating parameters such as for example throughput requirements and/or temperature. However, the look-up table is finalized at the design phase of the electronic system and therefore the look-up table has to include a safety margin to overcome dynamic changes and post-design variables. This safety margin leads to energy loss at run time.
Technical solutions usable in conjunction with and/or related to optimizing energy consumption are described for example in the following publications: U.S. Pat. Nos. 8,924,902, 8,237,477, and 8,072,796.